This image from the Cassini spacecraft shows four moons huddled near Saturn’s multi-hued disk. The coloration of the planet’s northern hemisphere has changed noticeably since the Cassini spacecraft’s arrival in orbit in mid-2004. Giant Titan (5,150 kilometers, or 3,200 miles across), with its darker winter hemisphere, dominates the smaller moons in the scene. Beneath and left of Titan is Janus (181 kilometers, or 113 miles across). Mimas (397 kilometers, or 247 miles across) appears as a bright dot close to the planet and beneath the rings. Prometheus (102 kilometers, or 63 miles across) is a faint speck hugging the rings between the two small moons. This view looks toward the unilluminated side of the rings from less than a degree above the ringplane. This image was taken by Cassini’s wide-angle camera on October 26, 2007, at a distance of approximately 1.5 million kilometers (920,000 miles) from Saturn and 2.7 million kilometers (1.7 million miles) from Titan.

Representing the international character of many NASA planetary missions since Voyager, Cassini-Huygens, a joint effort of NASA, the European Space Agency, and Italian Space Agency, has also proved to be an incredible success. It seems appropriate to recall this mission since Cassini, the first spacecraft to orbit Saturn, arrived there on July 1, 2004. This mission also sent a probe (Huygens) to the surface of Saturn’s moon Titan on January 15, 2005. Huygens was a product of the European Space Agency, and the first outer planetary mission by that organization. I will write specifically about Huygens in another blog post.

But even before its Saturnian encounter, the Cassini mission advanced science by finding individual storm cells of upwelling bright-white clouds in dark “belts” in Jupiter’s atmosphere, and by conducting a radio signal experiment on October 10, 2003 that supported Einstein’s theory of general relativity.

At Saturn, Cassini has discovered three new moons (Methone, Pallene, and Polydeuces), observed water ice geysers erupting from the south pole of the moon Enceladus, obtained images appearing to show lakes of liquid hydrocarbon (such as methane and ethane) in Titan’s northern latitudes, and discovered a storm at the south pole of Saturn with a distinct eye wall. Cassini, like Galileo at Jupiter, has demonstrated that icy moons orbiting gas giant planets are potential refuges of life, and attractive destinations for a new era of robotic planetary exploration.

It seems appropriate to recognize the important of the Cassini-Huygens mission to Saturn at this point when it arrived at the planet. It’s success was the result of large-scale flagship planning and operations in an international setting between NASA and other space organizations. Some have derided these missions as “Battlestar Galacticas” that cost too much and are too slow in their development; others emphasize that these costly and time-consuming missions provide more good science over a longer period than smaller, quicker projects. The reality is that both sides are correct, and that the best answer is a mix of missions of a large, complex variety but also smaller, more focused projects. Regardless of where one comes down on this debate, no one can deny that Cassini has been a stunning planetary science mission that has made a fundamental impact on our knowledge of this unique planetary system. So, happy anniversary Cassini; and I hope there are many more.

Cassini performed two flybys of Venus and one of Earth to obtain the velocity needed to leave the inner solar system. It then flew by Jupiter before finally arriving at Saturn in July 2004, more than six years after launch.